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By Christopher Vaughan

With populations and concomitant demands for energy growing at rates that existing resources are not projected to meet indefinitely, the tide may be turning for technologies tapping new and abundant energy sources. No larger reservoir of potential exists than the one covering 70 percent of the globe’s surface. Ocean energy, long dreamed of but to date the subject of insufficient investment, may be at least one of the answers to the energy-shortage forecast to challenge future growth. It is almost certainly the most renewable, as long as the globe keeps spinning.

The complex relationship between energy and water promises to be one of the most significant factors in global development going forward. Freshwater supplies are endangered in general, but the equation varies greatly by region and state of development. Most uses of water in energy production result in electricity generation, typically using hydraulic turbines in dammed rivers. Energy derived from water sources varies from an almost complete reliance on hydroelectric power in many nations to relatively scanty percentages in the United States (about 6.6 percent) and Israel (less than 1 percent). Worldwide, hydroelectric sources comprise 20 percent of energy supplies.

While imposing considerable impacts upon the environment, hydroelectric constitutes by far the largest source of renewable energy in the world. Small-scale hydroelectric-energy production can be obtained from any source of running water, and while it is not yet a significant factor in energy production, it has one of the best returns on investment of any renewable-energy source, with hydro systems available at roughly 10 percent of the cost of a photovoltaic solar system of comparable energy output.

Other uses of water to generate energy offer promising possibilities, but none have yet emerged to play significant roles in the portfolios of the United States, Israel, or, indeed, any other nation. Still, the future may see increasing shares of energy supply coming from water-based solutions. These range from the obvious — such as tidal power, which draws upon the relationship between the Earth and the moon — to hybrid categories, such as wave energy and biofuels, natural gas, coal and tar-sands oil, all of which can draw heavily upon water supplies to extract and convert into energy. Traditional fossil fuels, nuclear power and geothermal involve use of water in production. Balancing human needs for fresh drinking water with energy and agricultural uses will pose one of the great challenges of coming decades.

The oceans may provide solutions. Ocean energy, which converts naturally occurring processes into storable energy, is in the early stages of development and thus constitutes a negligible share of national energy production in any of the locales where it is being tested, but it has been estimated that it could eventually meet up to 10 percent of worldwide energy demand. Such estimates include utilization of everything from thermal properties, salinity gradients and tidal patterns to the ocean’s most visible dimension, the surface waves that provide the conversion methods now closest to commercial viability.

Already, desalinization plants can convert seawater to freshwater uses, but at a high cost in energy — although a wave-powered desalinization project in Mexico seeks to ameliorate that drain. At the same time, energy derived from the seas could provide significant power solutions once technological progress advances to a point where costs translate into prices competitive with conventional sources. Scores of projects currently compete to produce the best results in the emerging marketplace, with no clear leader yet established. In the United States, numerous trial projects are under way, while Israel already has seen its first wave-energy system — a pilot project under the auspices of S.D.E. Energy — at Jaffa’s port. S.D.E. says that its design for only 10 percent of the system’s parts to be submerged increases durability, a key element in the sustainability of ocean-power projects. S.D.E. is awaiting financing to construct a larger-scale 50-megawatt project in Jaffa.

Compared with other forms of offshore renewable energy, such as solar photovoltaic, wind, or ocean current, wave energy is continuous but highly variable — although wave levels at a given location can be confidently predicted several days in advance, enhancing the likelihood of effective integration into a multi-pronged energy strategy. Wave energy’s enormous potential, given the sheer volume of the oceans, is undeniable, but its costs include electricity transfer from the site of generation and potentially significant maintenance and repair bills due to the harsh treatment the seas can mete out to equipment. Wave energy’s variability may be its largest liability. Its greatest potential is in areas of strong wave activity, but larger waves threaten the lifespan of energy-collection systems, while less destructive smaller waves deliver less energy. Deep-water waves may offer a better equation than near-shore waves, but no systems focused on such sources have been steadily employed to date.

The effects of wave energy systems on the environment include potential interference with wildlife and coastline sediment accumulation patterns, but on the whole the pollution and environmental impacts appear relatively minor.

Wave-energy conversion devices of various sorts have been shown to be technically feasible, but from terminators — devices oriented perpendicular to the direction of wave propagation, which use trapped subsurface water to drive oscillating water columns like pistons — to attenuators —devices oriented parallel to the direction of wave propagation, which convert surface waves into energy using flexible floating devices — the relative values of extraction processes being tested remain variable. Buoys and other floating or partly submerged devices drive electromechanical or hydraulic energy converters, while overtopping devices use reservoirs in which water is used to drive hydro turbines or other conversion devices. Hybrids and new devices continue to emerge in an unsettled marketplace.

Tides and river and ocean currents offer additional potential, with tidal power plants now established in many locations worldwide. Dynamic tidal power, which envisions long dams headed straight out into the ocean with a perpendicular barrier at the end forming a T-shaped dam that does not actually enclose any area, is new and untested, but its system of drawing energy as the horizontal acceleration of the tides is blocked by the dam is thought to hold promise, since the water-level differential, or head, is converted to energy as water passes through turbines installed in the floating dam. The theoretical advantages of working on the envisioned scales of 30 to 60 kilometers are not testable at smaller scales; however, posing problems for gaining buy-in by the large institutional forces that would logically take on any such venture.

Wave energy and tidal energy both create electricity, but in different ways. While wave energy captures the energy in the vertical rise and fall of waves, tidal energy captures the energy in the horizontal ebb and flow of the tides.

The vast resources of the oceans may yet prove an answer for many energy problems, but it may require investments of similarly grand scale to fully realize the potential in easy view of the coasts where most of the world’s populations are concentrated. The political will to take such chances may well be the most valuable renewable resource of all, on par with the water from which the users of the world’s energy resources once emerged.

Dr. Christopher Vaughan is a scholar, activist and award-winning journalist. As a Pulitzer Prize finalist, foreign correspondent, editor, professor and MoveOn.org organizer, he has written about energy and the environment in the context of political and economic struggle.